Problem: Suppose the circumference of a circle is ${6\pi}$. What is its area?
${c = 6\pi}$ ${K = 9\pi}$ First, find the radius: $r = c/2\pi = {6\pi}/2\pi = {3}$ Now find the area: $K = \pi r^2$, so $K = \pi \cdot {3}^2 = {9\pi}$.